Pneumatic tires, which are pressurized air-filled tires, have proven valuable in providing a comfortable ride with optimal load-carrying capabilities for a variety of vehicles. Consequently, pneumatic tires have become the standard in virtually all passenger tire and high speed wheel applications, and more specifically, in almost every aircraft, automobile, truck, van, bicycle and the like, where ride quality and comfort is an important part of the performance of the vehicle. Pneumatic tires have also been successful in low speed applications, such as on tractors, carts, and the like, where load carrying capability is important. However, the tire carcass in pneumatic tires are susceptible to cracks, punctures and/or other damage causing release of the air trapped inside and resulting in the tire going flat. A flat tire may simply cause inconvenience, by requiring a repair and/or loss of use of the vehicle, or may render the tire unusable and cause more of a financial burden, particularly in industrial applications, by requiring costly tire replacement. The consequences of a flat tire might also be far more dire. For example, a tire suddenly going flat, such as a blow out, can be life threatening, particularly to passengers traveling in the vehicle at high speeds.
As an optional substitute to pneumatic tires, non-pneumatic tires have been developed and utilized in a wide variety of applications. Non-pneumatic tires are typically solid tires having no hollow or air-pressurized cavities or chamber(s) therein, as opposed to semi-pneumatic tires, which are partially filled with air. Being of zero pressure, a non-pneumatic tire is generally deflation-proof, due to the lack of air pressure. The first non-pneumatic tires developed were solid tires formed generally from natural rubber. However, rubber tires require thick walls and thick tread regions to provide load carrying capability comparable to pneumatic tires, and such added rubber results in an undesirable increase in the weight of the tire and a compromise in its ride quality.
More technically advanced non-pneumatic tires have been proposed utilizing various materials having greater performance characteristics than the previously developed rubbers. Particularly, solid non-pneumatic tires formed from polymeric materials, such as polyurethane, have been developed. However, while solid polyurethane tires are capable of carrying higher loads with a smoother ride, they are generally heavier and prone to faster wear and breakdown than pneumatic tires. In addition, solid polyurethane tires are subject to “chunking” (sections separating from the tire body) and are easily cut when used in aggressive applications and/or on rugged terrain. Further, solid polyurethane tires also have reduced traction characteristics as well as UV and ozone resistance when compared to pneumatic tires.
More recently, conventional pneumatic tire shells or casings have been filled with a solid composition, such as a polyurethane elastomer, to produce deflation-proof, non-pneumatic tires in an attempt to overcome the weaknesses of previously developed non-pneumatic tires. For example, U.S. Pat. Nos. 4,943,233, 4,855,096, and 5,906,836 all disclose the use of polyurethane foams as filling materials for a conventional pneumatic tire to produce a non-pneumatic tire, such as a bicycle tire.
In conjunction with producing such non-pneumatic tires, new methods and fill compositions have been proposed. For example, U.S. Pat. No. 6,187,125, issued to Rustad, discloses a fill composition and method for producing a non-pneumatic tire filled with the cured composition. The fill composition is a mixture of a polyisocyanate having an average functionality of at least 2.3; a high molecular weight polyol having a hydroxyol number in the range of about 20 to about 31 and having an actual functionality of greater than 2.1; 6 to 65 weight percent of a polar plasticizing extender oil; and optionally a polyamine in an amount less than 0.5 weight percent. The mixture is cured in the presence of a catalyst to form a resilient polyurethane elastomer having a vertical rebound of greater than about 60% based on ASTM D2632 and Durometer hardness in the range of about 5 to 60 (as measured by the Shore A method).
U.S. Pat. No. 6,450,222, issued to Fleming, discloses a non-pneumatic tire having an elastomeric portion encompassing the tread and a radially inward foam portion. The non-pneumatic tire may be formed from a multi-shot process in a spin cast procedure.
U.S. Pat. No. 5,080,737, issued to Shoner, discloses a method of filling a tire with a composite foam to eliminate rapid deflation “blow-outs”. The composite foam tire filling is comprised of a multiplicity of preconstructed, hollow, pressurized elastomeric, one-piece, seamless cells bonded together into a configuration whereby substantially all of the exterior cell wall surface of all cells in the filling is engaged with portions of the exterior cell wall surfaces of the surrounding cells.
U.S. Pat. No. 5,229,047, issued to Becker, discloses a method and apparatus for producing foam elastomer tires for various uses including bicycles and wheel chairs. The method involves spin casting the tires in a mold and filling the mold with a preblended liquid foamable material that is poured directly into the mold or onto a surface immediately adjacent to the mold, prior to entry into the mold.
U.S. Pat. No. 4,094,353, issued to Ford, discloses a process for puncture-proofing a pneumatic tire mounted on a wheel rim comprising filling the tire with a cross-linked mixture of polyoxypropylene polyether polyol and diphenylmethane diisocyanate to form a resilient solid polyurethane fill material inside the tire.
U.S. Pat. No. 4,909,972, issued to Britz, discloses a method of making a solid core locatable between a wheel rim and a tire fitted to the rim, the core formed by introducing a foamable composition into a mold cavity having a substantially inflexible mold surface, and allowing the composition to foam and fill the cavity, prior to removal for placement in a standard tire carcass.
U.S. Publication No. 2002/0129883, issued to O'Coin, discloses a tire including a tread region, a rim region, and a further region between the tread and the rim region containing a foamed rubber.
U.S. Pat. No. 5,605,657, issued to Nybakken, discloses an industrial solid tire for heavy-load, off-road use having a heat-cured, silicone containing polyurethane therein, produced by a batch method.
U.S. Pat. No. 5,073,444, issued to Shanelec, discloses a molded polypropylene foam tire core suitable for all types of wheels. The core may be inserted, in one or more sections, into a pneumatic-type tire casing and mounted on a wheel rim to provide puncture-proof and rupture-proof internal support for said tire casing.
U.S. Pat. No. 5,681,411, issued to O'Coin, discloses a pneumatic tire having a plurality of layers of high density foam rubber formed therein and methods of manufacturing and installing the layers in the tire.
Despite generally having a harder ride and, in some cases, adding more weight to the vehicle in comparison to a pneumatic tire, the availability of deflation proof non-pneumatic tires is generally more economical and practical, relative to pneumatic tires, for many uses and applications in various industries including mining, scrap yards, military, and heavy construction. Non-pneumatic tires eliminate the problem of a flat and/or blowout by eliminating the need for pressurized air. Thus, non-pneumatic tires overcome the inherent problems with pneumatic tires, as discussed above.
However, many of the desirable performance characteristics found in pneumatic tires have not been duplicated in the previously proposed non-pneumatic tires. In particular, the performance characteristics of cushioning ability, roll ability, noise and vibration reductions have not been equaled. Thus, there is a desire to replicate the pneumatic tire characteristics and properties in a non-pneumatic tire. In addition, many of the compositions and methods previously proposed for producing non-pneumatic tires involve polymers which provide an advantage in one property while suffering from a weakness in another property. For example, one polymer may exhibit superior vibration and noise characteristics while possessing an inferior load carrying capacity. Further, the overall costs of previously proposed non-pneumatic tires by methods of producing same has generally increased with the added step of filling, containing and curing the fill material within a pneumatic tire shell. Also, many of the methods previously proposed are unreliable in that they fail to ensure a complete fill without voids, are relatively expensive, and/or raise various safety and/or environmental concerns.
Thus, there exists a need to provide non-pneumatic tires having performance characteristics similar to those of pneumatic tires without the disadvantage of flats and blow-outs. There is also a need to provide a high quality, zero pressure, air-free non-pneumatic tire with improved load handling capacity and without a significant compromise in ride quality. There is a further need to provide non-pneumatic tires having beneficial qualities in a more simplistic, convenient and cost effective manner than previously proposed methods.